Not applicable.
1. Field of the Invention
This invention relates to determination of characteristics of material, for example automatic inspection and sorting of discrete objects of differing compositions, e.g. waste objects.
2. Description of the Related Art Including Information Disclosed Under 37CFR 1.97 and 1.98
With the recent focus on collection and recycling of waste, the cost effectiveness of waste sorting has become an essential economic parameter.
In the xe2x80x9cDual Systemxe2x80x9d in Germany all recyclable xe2x80x9cnon-biologicalxe2x80x9d packaging waste excluding glass containers and newsprint is collected and sorted in more than 300 sorting plants.
Objects can be sorted on the basis of:
Size
Density/weight
Metal content (using eddy current effect)
Ferrous metal content (using magnetic separation)
but most objects such as plastics bottles and beverage cartons are today sorted out manually. Some beverage cartons contain an aluminium barrier and by eddy current induction they can be expelled from the waste stream. Generally, beverage cartons in their simpler form present a composite object consisting of paperboard with polymer overcoats on both their inside and outside surfaces.
A system known in Europe for separating-out from a stream of waste a fraction comprised of polymer-coated paperboard objects consists simply of operatives picking out such objects by hand, the operatives visually identifying the polymer-coated paperboard objects. Such manual picking-out of cartons can have a very high percentage hit rate, but is undesirably slow. We are aware of a proposal in Europe for a system in which an operative visually identifies polymer-coated paperboard objects and controls a robot to perform the picking-out of the objects in question.
Such robotic picking-out of cartons could have a very high percentage hit rate, but would be undesirably slow.
To make a positive identification by automatic means is very difficult. U.S. Pat. No. 5,615,778 discloses a process to sort waste mixtures by irradiating the waste objects with electromagnetic and/or acoustic waves, by picking up the waves emanating from each irradiated waste object in a signal processor to identify it, and by transmitting signals from the signal processor to a separator which sorts out the identified waste object. The apparatus may include a video camera to pick up the waves emanating from the waste object. A still photo camera, an UV or IR receiver, or a microphone, can be substituted for the video camera. One or more characterizing features of the object are detected and then evaluated by the signal processor. Examples of such characterizing features are the external shape of the object such as, for instance, the shape of bottles, cups, tubes and cubic shapes, as well as characteristic lettering, product names, company or manufacturer names, trademarks, colours and the like, which are present on the object. However, physical shape is normally quite distorted, making recognition very complex unless the printing pattern is made in a specially recognisable way, or the carton is equipped with a recognisable marker or tracer, which depends upon the willingness of manufacturers and their customers to limit particular markings to goods of particular compositions.
DE-A-3346129 discloses a system for sorting refuse containing waste glass, particularly hollow waste glass, in which system items of refuse of optional minimum particle size are separated from the rest of the refuse, those items are conveyed along a track in at least one line, pieces of green, brown and clear scrap glass are identified while being conveyed along the track, and the identified pieces are separately ejected as fractions after a time delay. In addition to the items consisting of flat glass, pieces of metal, ceramics, cork, plastics or clay are also identified, whereafter they and any pieces not identified are separated consecutively on further sections of the track (after the track section upon which the glass and other identified pieces are identified). The or each line in the track has its own colour recognition unit at a recognition station. Each stream of waste appears to consist of a single row of items. There may be a plurality of tracks in the form of respective conveyor belts advancing parallelly to each other and in a common direction. Separated-out fractions may be conveyed away by respective conveyor belts extending perpendicularly to the tracks.
JP-A-5-169037 discloses a system for accurately separating opaque foreign matter from transparent bodies, while they are being dropped from a conveyor. The falling transparent bodies and the opaque foreign matter are horizontally and linearly scanned by a laser beam, and the reflected light is detected by a CCD (cathode coupled device)-type image sensor. Whether the image is of the transparent body or opaque foreign matter is discriminated for each CCD block containing N-units, and air is injected from one nozzle block corresponding to the CCD block containing the opaque foreign matter and from the adjacent nozzle block.
Several sorting systems exist today that can sort a number of different plastics bottles/objects from each other when they arrive sequentially (i.e. one-by-one). The detection is based on reflected infrared spectrum analysis. To separate the various polymers a quite elaborate variance analysis has to be performed and thus detection systems become expensive. The objects being fed sequentially pass beneath the infrared spectral detector whereby infrared is shone onto the objects and the relative intensities of selected wavelengths of the infrared radiation reflected are used to determine the particular plastics compound of the plastics passing beneath the detection head. Downstream of the detection head are a number of air jets which blow the individual plastics objects into respective bins depending upon the plastics which constitutes the majority of the object.
A similar system is disclosed in U.S. Pat. No. 5,134,291 in which, although the objects to be sorted can be made of any material, e.g. metals, paper, plastics or any combination thereof, it is critical that at least some of the objects be made predominantly from PET (polyethylene terephthalate) and PS (polystyrene) as well as predominantly from at least two of PVC (polyvinyl chloride), PE (polyethylene) and PP (polypropylene), for example objects including: an object made predominantly from PET, an object made predominantly from PS, an object made predominantly from PVC and an object made predominantly from PE. A source of NIR (Near Infra Red), preferably a tungsten lamp, radiates NIR onto a conveyor sequentially advancing the objects, which reflect the NIR into a detector in the form of a scanning grating NIR spectrometer or a diode array NIR spectrometer. The detector is connected to a digital computer connected to a series of solenoid valves controlling a row of air-actuated pushers arranged along the conveyor opposite a row of transverse conveyors. The diffuse reflectance of the irradiated objects in the NIR region is measured to identify the particular plastics of each object and the appropriate solenoid valve and thus pusher are operated to direct that object laterally from the conveyor onto the appropriate transverse conveyor. The computer can manipulate data in the form of discrete wavelength measurements and in the form of spectra. A measurement at one wavelength can be ratioed to a measurement at another wavelength. Preferably, however, the data is manipulated in the form of spectra and the spectra manipulated, by analogue signal processing and digital pattern recognition, to make the differences more apparent and the resulting identification more reliable.
DE-A-4312915 discloses the separation of plastics, particularly of plastics waste, into separate types, on the basis of the fact that some types of plastics have characteristic IR spectra. In the IR spectroscopic procedure, the intensity of diffusely reflected radiation from each sample is measured on a discrete number of NIR wavelengths simultaneously and the intensities measured are compared. Measurements are taken on wavelengths at which the respective types of plastics produce the minimum intensities of reflected radiation. If, for example, three different plastics are to be separated, each sample is measured on three wavelengths simultaneously, whereby one type of plastics is identified in a first comparison of the intensity of the reflected radiation on the lowest wavelength with that of the second-lowest wavelength and the other two types of plastic are determined in a second comparison of the greater intensity on one wavelength in the first comparison with the intensity on the third wavelength. To measure the light on particular wavelengths, respective detectors can have narrow band pass filters for the respective requisite wavelengths, and respective constituent cables of a split optical fibre cable are allocated to the respective detectors, the cable entry lying in the beam path of a lens for detecting the light reflected from the sample. Alternatively, a light dispersing element, e.g. a prism or grid, is placed in the beam path after the lens and several detectors are arranged to detect the NIR of the requisite wavelengths. Sorting facilities are controlled by utilising the detection data obtained by the comparisons. As a further example, five differing plastics, namely PA (polyamide), PE, PS, PP and PETP, may be separated, utilising measurement points at five differing wavelengths between 1500 nm. and 1800 nm.
EP-A-557738 discloses an automatic sorting method with substance-specific separation of differing plastics components, particularly from domestic and industrial waste. In the method, light is radiated onto the plastics components, or the plastics components are heated to above room temperature, light emitted by the plastics components and/or light allowed through them (in an embodiment in which light transmitted through the components and through a belt conveying them is measured) is received on selected IR wavelengths, and the material of the respective plastics components is identified from differences in intensity (contrast) between the light emitted and/or absorbed, measured on at least two differing wavelengths. The light emitted or allowed through is received by a camera which reproduces it on a detector through a lens. A one-dimensional line detector is usable, although a two-dimensional matrix detector or a one-element detector with a scanning facility can be employed. In order that the camera may receive the light on selected IR wavelengths, interference filters may be mounted either in front of the light source or in front of the lens or the detector. In an example in which the material of the plastics components is identified from the differences in intensity of emitted light at two differing wavelengths, the wavelengths are chosen to produce maximum contrast. This means that one wavelength is selected so that maximum intensity of the emitted light is obtained at a specified viewing angle, whereas the other wavelength is selected so that minimum intensity is obtained at that viewing angle. Changing of wavelengths may be achieved by mounting the filters on a rotating disc, with the frequency of rotation being synchronized with the imaging frequency of the detector. Alternatively, an electrically triggered, turnable, optical filter may be employed. The electrical signals generated by the detector are fed to an electronic signal processor, digitised, and subsequently evaluated by image processing software. It is ensured that the plastics components are at approximately the same temperature at the time of imaging, as differences in contrast can also be caused by temperature differences. The belt should consist of a material which guarantees constant contrast on individual wavelengths.
There is also previously known a system in which infrared spectral detection is performed from below the objects, with the objects passing sequentially over a hole up through which the IR is directed. Again, the infrared reflected is used to sort the objects according to the various plastics within the respective objects.
U.S. Pat. No. 5,260,576 and EP-A 484 221 disclose a method and apparatus for distinguishing and separating material items having different levels of absorption of penetrating electromagnetic radiation by utilising a source of radiation for irradiating an irradiation zone extending transversely of a feed path over which the material items are fed or passed. The irradiation zone includes a plurality of transversely spaced radiation detectors for receiving the radiation beams from the radiation source. The material items pass through the irradiation zone between the radiation source and the detectors and the detectors measure one or more of the transmitted beams in each item passing through the irradiation zone to produce processing signals which are analyzed by signal analyzers to produce signals for actuating a separator device in order to discharge the irradiated items toward different locations depending upon the level of radiation absorption in each of the items. The disclosure states that mixtures containing metals, plastics, textiles, paper and/or other such waste materials can be separated since penetrating electromagnetic radiation typically passes through the items of different materials to differing degrees, examples given being the separation of aluminium beverage cans from mixtures containing such cans and plastic containers and the separation of chlorinated plastics from a municipal solid waste mixture. The source of penetrating radiation may be an X-ray source, a microwave source, a radioactive substance which emits gamma rays, or a source of UV energy, IR energy or visible light. One example of material items which are disclosed as having been successfully separated are recyclable plastic containers, such as polyester containers and polyvinyl chloride (PVC) containers, which were separated using X-rays.
In an eddy current system for ejecting metal from a stream of waste, the discharge end roller of a belt conveyor normally contains a strong alternating magnetic field generated by permanent magnets contained within and distributed along the roller and counter-rotating relative to the sense of rotation of the roller. This field ejects metallic objects to varying degrees depending upon the amount and the conductivity of the metal of the object. Since metallic objects in which the metal content is small, for example post-consumer packaging cartons of a laminate consisting of polymer-coated paperboard and aluminium foil, are only weakly affected by the magnetic field, such cartons, if in a greatly deformed condition, tend not to be separated-out by the eddy-current ejection system.
Another known system uses an electromagnetic field for eddy current detection through induction of eddy currents in the metal in metallic objects and the detection output is used to control an air jet ejection arrangement but this time the objects are caused to queue up one after another in single lines.
Various systems are known for automatic inspection of a continuous strip of sheet material. One system includes a mechanical scanner reciprocated across the width of the strip as the latter advances past the scanner. Light containing IR is shone onto a transverse section of the strip and the scanner includes a transducer which detects the reflected IR at a plurality of locations across the section and emits electrical signals representing, for instance, the polymer layer thickness of a polymer layer/paperboard layer laminate. This is employed in a laminating machine to control the thickness of polymer deposited onto the paperboard.
U.S. Pat. No. 4,996,440 discloses a system for measuring one or a plurality of regions of an object to be able to determine one or a plurality of dimensions of the object. In one example, the system utilises a mirror arrangement for transmitting pulsed laser light so that the light impinges downwards upon the object and for receiving the upwardly reflected light. The system includes a laser, a rotating planar mirror and a concave frusto-conical mirror encircling the planar mirror, which serve for directing the light beam towards the object. The frusto-conical mirror, the planar mirror and a light receiver serve for receiving light beams which are reflected from the object. Electronic circuitry connected to the light receiver serves for calculating the travel time of the beam to and from the object, with a modulator causing the light beam to be modulated with a fixed frequency and the rotating planar mirror and the frusto-conical mirror causing the light beam to sweep across the object at a defined angle/defined angles relative to a fixed plane of reference during the entire sweeping operation.
According to a first aspect of the present invention, there is provided a method of separating a fraction comprising polymer-coated paperboard objects from a stream of waste, comprising advancing said stream through a detection station and separating the polymer-coated paperboard objects from the stream, wherein at said station a determination is made, using substantially invisible electromagnetic radiation, solely as to whether a portion of said waste is or is not a polymer-coated paperboard object.
Owing to this aspect of the invention, it is possible to minimize the number of radiation wavelengths required to be analyzed.
According to a second aspect of the present invention, there is provided a method of automatically inspecting matter for varying composition, comprising passing a stream of said matter through a detection station, emitting a detection medium to be active at a transverse section of said stream at said detection station, wherein said medium is varied by variations in the composition of said matter at said transverse section, receiving the varied medium from over substantially the width of the stream at a receiving device, and generating detection data in dependence upon the variations in said medium, wherein said transverse section comprises a multiplicity of individual detection zones distributed across substantially the width of said stream, and the detection data from said individual detection zones is used to construct a two-dimensional simulation of said matter passing through said detection station, said detection medium comprising electromagnetic radiation which irradiates said section, said generating including determining the intensity of electromagnetic radiation of selected wavelength(s) reflected from portions of said stream distributed across said stream, and said determining being performed for each detection zone in respect of a plurality of wavelengths simultaneously.
The method may comprise advancing the stream through a detection station, emitting a detection medium to be active at a transverse section of said stream at said detection station, wherein said medium is varied by variations in the composition of the stream at said transverse section, receiving the varied medium over substantially the width of the stream at receiving means which physically extends across substantially the width of said stream and which transmits the varied medium towards detecting means, detecting the varied medium at said detecting means and generating detection data in dependence upon the variations in said medium, the varied medium converging upon itself during its travel from said receiving means to said detecting means.
Apparatus for performing the method may comprise advancing means for advancing the stream, a detection station through which said advancing means advances said stream, emitting means serving to emit a detection medium to be active at a transverse section of said stream at said station, receiving means at said station arranged to extend physically across substantially the width of said stream and serving to receive detection medium varied by variations in the composition of said stream at said section, detecting means serving to generate detection data in dependence upon the variations in said medium, and data-obtaining means connected to said detecting means and serving to obtain said detection data therefrom, said receiving means also serving to transmit the varied medium to said detecting means such that the varied medium converges upon itself during its travel from said receiving means to said detecting means.
It is thus possible for the stream to be relatively wide, so that the inspection rate can be increased, and yet the capital cost of the detecting means need not increase in the same proportion.
The detection medium can be electromagnetic radiation, for example IR or visible light to detect variations in constituency or colour, or an electromagnetic field to detect metal portions of the stream, e.g. in sorting of materials. A wide variety of materials may be sorted from each other, but particularly plastics-surfaced objects sorted from other objects. For the present automatic sorting, the objects must be distributed in substantially a single layer.
Preferably, for sorting of objects, the objects are advanced through the detection station of an endless conveyor belt.
For a polymer, two or more detection wavelength bands in the NIR region of 1.5 microns to 1.85 microns can be employed.
For a laminate comprised of a first layer and a second layer underneath said first layer and of a material having a spectrum of reflected substantially invisible electromagnetic radiation significantly different from that of the material of the first layer, the spectrum of substantially invisible electromagnetic radiation, particularly IR, reflected from such laminate can be readily distinguishably different from the spectrum of that radiation reflected from a single layer of the material of either of its layers.
Using substantially invisible electromagnetic radiation, particularly IR, has the advantage of permitting more effective determination of the composition of the first layer.
In cases where the first layer is a polymer, e.g. polyethylene, for the diffusely reflected IR from the substrate to be sufficient for detection purposes, the first layer should be no more than 1 mm. thick. Its thickness is advantageously less than 100 microns, preferably less than 50 microns, e.g. 20 microns.
For a laminate comprised of polyethylene on paperboard, a first wavelength band centred on substantially 1.73 microns is employed, as well as a second wavelength band centred less than 0.1 microns from the first band, for example at about 1.66 microns. The transverse section of the stream may comprise a multiplicity of individual detection zones distributed across substantially the width of said stream, and the detection data from said individual detection zones be used to construct a two-dimensional simulation of said matter passing through said detection station.
Typically, there could be a transverse row of some 25 to 50 detection points for a stream 1 m. wide. A central detection system can be applied to xe2x80x9cservexe2x80x9d all 25 to 50 detection points if there is sufficient IR intensity across the width of the stream from a single or multiple IR source or even if there is an infrared source at each detection point. Optical fibres may lead the reflected IR from the detection points to this central detection system. However, a system of IR reflectors is preferred to optical fibres, since a reflector system is less expensive, allows operation at higher IR intensity levels (since it involves lower IR signal losses) and is less demanding of well-defined focal depths. If the stream moves at some 2.5 m/sec. and the system is capable of 100 to 160 scans across the stream each second, then detections can be made at a spacing of some 2.5 to 1.5 cm along the stream. When each scan is divided into 25 to 50 detection points, detections can be made in a grid of from 1.5xc3x972.0 cm. to 2.5xc3x974.0 cm.
The transverse scanning of the moving stream makes it possible to construct a two-dimensional simulation which can be analyzed using image processing. In this way it is possible to detect:
matter composition, e.g. thickness, and position in the stream
shape and size of composition variation
several composition variations substantially simultaneously.
The detection data processing system will determine wanted/unwanted composition at each point.
In separating beverage cartons from a stream of waste, the signals from each of the wavelength bands are combined using signal processing for each detection. The two-dimensional simulation which is built up as the stream passes the detection station can be processed using robust statistical data analysis. For example, a logical rule may be applied where a minimum cluster of positive detections, for instance 3xc3x973, is required before the system recognises a possible beverage carton. In high speed systems (e.g., 2.5 m./sec. belt speed) only slight air pulses (an air cushion) are required to alter the carton exit trajectory from the belt sufficiently that they can land in a bin separate from other objects dropping freely. Normally, some 15-30 positive detections are made on a 1 liter carton. The peripheral detection points in the clusters can thus advantageously be disregarded, only initiating the air pulses according to the interior detection points, so securing more lift than tilt.
In slower speed systems (e.g., 0.2-0.5 m/sec belt speed) more positive air ejection pulses may be required to expel the cartons from the remaining stream. This requires air pulses hitting the cartons near their centres of gravity to avoid uncontrolled ejection trajectories.
Although an advantage of arranging the detection of objects from underneath (rather than above) the waste stream is that it gives as uniform a distance from detection point to object as possible, it has disadvantages which more than outweigh that advantage. By irradiating the waste objects on a conveyor belt with radiation from above and by utilising a reflector system to select that portion of the reflected radiation which propagates roughly vertically, the system can be made very focusing insensitive.
In addition to spectral sensing devices, electromagnetic sensing devices may be employed at a metal-detection station. By means of an antenna extending across the advancing means, an alternating electromagnetic field can be set up across the advancing means. By providing as many eddy current detection points (in the form of individual detection coils) across the advancing means as there are spectral detection points a simultaneous metal detection can be performed at very low additional cost.
Thereby, with a waste stream including polymer-coated beverage cartons, and with several air jet arrays arranged one after another it becomes possible to sort out:
beverage cartons without an aluminium barrier
beverage cartons with an aluminium barrier
other metal-containing objects.
With a more elaborate spectral analysis it also becomes possible to identify and sort out the type of polymer in a plastics object. The system could hence be applied to sorting into separate fractions the various plastics types occurring.
An important cost factor in the spectral analysis system, whether mirror systems or fibre optic systems are used, is the method chosen to xe2x80x9cservexe2x80x9d the detection points. A preferred embodiment of the method comprises irradiating with electromagnetic radiation comprising substantially invisible electromagnetic radiation a section of said stream at said station, scanning said section and determining the intensity of substantially invisible electromagnetic radiation of selected wavelength(s) reflected from portions of said stream, and obtaining detection data from said detection station, said scanning being performed in respect of a plurality of discrete detection zones distributed across said stream and said determining being performed for each detection zone in respect of a plurality of said wavelengths simultaneously.
It is thus possible to increase the rate of reliable detection.
One device scanning all of the detection points should be the simplest and least expensive. A high-quality, high-speed device is required, but one optical separation unit with the required number of separation filters and detectors can then serve all detection points.
Frequency multiplexing IR pulses to all detection points is another alternative but this system would be more sensitive to interference and more costly than the first alternative.
Time multiplexing, whether of IR pulses to all detection points or of analysis of the diffusely reflected IR, can be somewhat simpler than frequency multiplexing, but implies that spectral identifications in the various wavelengths should be done sequentially, which could pose practical problems and limitations.
Determination that post-consumer beverage cartons contain polyethylene-coated paperboard can advantageously be done with only a few IR wavelengths analysed. Only NIR wavelengths seem to be required to be analysed, for example:
Wavelength no. 5, 2.028 microns, is quite moisture-sensitive and may advantageously be omitted. This will leave a very low number of wavelengths to be analysed and compared, thus increasing the maximum computational speed of the system considerably compared to existing systems designed for elaborate polymer absorption characteristic comparison.
Of the hereinbefore mentioned group of wavelengths Nos. 1 to 5, at least Nos. 2 and 3 are advantageously employed where IR radiation is utilized for separating-out of polyethylene-coated board, since, of common objects in a waste stream, paper and polymer-coated paperboard are the most difficult to distinguish between with IR detection and those two wavelengths give good discrimination between paper and polymer-coated paper.
Another preferred embodiment of the method comprises advancing through a detection station a first stream of matter, emitting detection medium to be active at a transverse section of said stream at said detection station, wherein said medium is varied variations in the composition of said matter at said transverse section, obtaining from said detection station first detection data as to a constituent of said first stream, advancing a second stream of matter through said detection station simultaneously with said first stream, emitting detection medium to be active at a transverse section of said second stream at said detection station, wherein the latter medium is varied by variations in the composition of matter of said second stream at the latter transverse section, and obtaining from said detection station second detection data as to a constituent of said second stream, and the varied medium from both of the first and second streams being received by a receiving device common to both streams.
The apparatus for performing that other preferred embodiment of the method comprises a detection station, first advancing means serving to advance through said station a first stream of matter, first emitting means serving to emit detection medium to be active at a transverse section of said stream at said detection station, a receiving device serving to receive detection medium varied by variations in the composition of said matter at said section, detecting means serving to produce first detection data as to a constituent of said first stream at said station, second advancing means serving to advance a second stream of matter through said station simultaneously with said first stream, and second emitting means serving to emit detection medium to be active at a transverse section of said second stream at said detection station, said receiving device serving also to receive detection medium varied by variations in the compositions of the matter at the latter section and being thus common to both of the first and second advancing means, and said detecting means serving to produce second detection data as to a constituent of said second stream.
Thereby, one-and-the-same detection station is employed for at least two streams simultaneously, so that the capital and running costs of inspection can be reduced compared with a case where the streams have respective detection stations.
The first and second streams can pass through the detection station in respective opposite directions or in a common direction. In the latter case, the streams can be conveyed on an upper run of an endless belt, with a partition along the upper run to keep the streams apart.
The streams can be inspected for respective constituents of differing compositions or of the same composition, in which latter case the second stream can be a separated-out fraction of the first stream, to produce a final separated-out fraction of increased homogeneity.